It is often necessary to plug or seal a tube or circular opening. Plugs can be used to seal bores formed in diesel engines, such as the plug disclosed in U.S. Pat. No. 6,053,992. Plugs are also used to seal tubes in heat exchangers. There are a wide variety of different methods used to seal such tubes. In certain applications, explosive devices are used to seal off a tube. But, this is very expensive. Mechanical devices can also be used; but, in high-pressure applications, these may fail.
A potentially useful plug to seal tubes is disclosed in Hall U.S. Pat. No. 5,189,789. This discloses the use of a memory metal or Nitinol plug. Memory metals are alloys that undergo a reversible transformation from an austenitic state to a martensitic state with changes in temperature. At colder temperatures, the alloy enters the martensitic state and reverts to the austenitic state at higher temperatures. A plug in the martensitic state can be bent or shaped. When the metal reverts to the austenitic state it reverts to its original shape.
U.S. Pat. No. 5,437,310 and U.S. Pat. No. 4,425,943, the disclosures of which are hereby incorporated by reference, disclose a plug formed from a tapered rod or wedge and a sleeve that fits over the exterior surface of the wedge. Moving the sleeve relative to the wedge causes the sleeve to expand enabling it to press against the side walls of the tube to plug the tube. Thermal expansion and contraction, however, can cause this plug assembly to fail.